The invention relates generally to semiconductor materials and, more particularly, to gallium nitride materials and methods of producing gallium nitride materials.
Gallium nitride materials include gallium nitride (GaN) and its alloys such as aluminum gallium nitride (AlGaN), indium gallium nitride (InGaN), and aluminum indium gallium nitride (AlInGaN). These materials are semiconductor compounds that have a relatively wide, direct bandgap which permits highly energetic electronic transitions to occur. Such electronic transitions can result in gallium nitride materials having a number of attractive properties including the ability to efficiently emit blue light, the ability to transmit signals at high frequency, and others. Accordingly, gallium nitride materials are being widely investigated in many semiconductor device applications such as transistors, field emitters, and optoelectronic devices.
Gallium nitride materials have been formed on a number of different substrates including silicon carbide (SiC), sapphire, and silicon. Silicon substrates are readily available and relatively inexpensive, and silicon processing technology has been well developed. However, forming gallium nitride materials on silicon substrates to produce semiconductor devices presents challenges which arise from differences in the lattice constant, thermal expansion, and band gap between silicon and gallium nitride.
Many semiconductor devices include at least two electrical contacts which, for example, provide electrically conducting contact to terminals of a power supply. In a typical device, current flows from a first contact (e.g., the anode) on the device to a second contact (e.g., the cathode) on the device. In certain devices, both the first and the second contacts are positioned on a topside (i.e., upper surface) of the device. Such devices are referred to as horizontally conducting devices because current flows horizontally through the device from the first contact to the second contact. In other devices, the first contact is positioned on the topside of the device and the second contact is positioned on a backside (i.e., bottom surface) of the device. Such devices are referred to as vertically conducting devices. In some cases, vertically conducting devices may be made smaller than an otherwise similar functioning horizontal device because horizontal devices include multiple topside contacts while vertical devices may require only one topside contact. Reducing device size may be advantageous because it increases the number of devices produced per unit area (wafer). Thus, vertically conducting devices may be preferred over horizontally conducting devices in certain applications.
The invention includes providing gallium nitride material devices having backside vias and methods to form the devices. The devices include a gallium nitride material formed over a substrate, such as silicon. The device also may include one or more non-conducting layers between the substrate and the gallium nitride material which can aid in the deposition of the gallium nitride material. A via is provided which extends from the backside of the device through the non-conducting layer(s) to enable electrical conduction between an electrical contact deposited within the via and, for example, an electrical contact on the topside of the device. Thus, devices of the invention may be vertically conducting. Exemplary devices include laser diodes (LDs), light emitting diodes (LEDs), power rectifier diodes, FETs (e.g., HFETs), Gunn-effect diodes, and varactor diodes, amongst others.
In one aspect, the invention provides a semiconductor structure. The semiconductor structure includes a substrate having at least one via extending from a backside of the substrate and an electrical contact formed in the via. The semiconductor structure also includes a gallium nitride material region formed over the substrate.
In another aspect, the invention provides a semiconductor structure. The semiconductor structure includes a silicon substrate having at least one via extending from a backside of the silicon substrate. The semiconductor structure also includes a gallium nitride material region formed over the silicon substrate.
In another aspect, the invention provides a vertically conducting semiconductor device. The semiconductor device includes a silicon substrate and a gallium nitride material region formed over the silicon substrate. The semiconductor device is capable of vertical conduction.
In another aspect, the invention provides a semiconductor structure. The semiconductor structure includes a silicon substrate and a gallium nitride material region formed over the silicon substrate. The semiconductor structure also includes a non-conducting layer formed between the gallium nitride material region and the silicon substrate, and an electrical contact formed within a via extending from a backside of the semiconductor structure through the non-conducting layer.
In another aspect, the invention provides a method of forming a semiconductor structure. The method includes forming a gallium nitride material region over a substrate, forming a via extending from a backside of the semiconductor structure, and forming an electrical contact within the via.
In another aspect, the invention provides a method of forming a semiconductor structure. The method includes forming a gallium nitride material region over a silicon substrate, and forming a via extending from a backside of the silicon substrate.
Among other advantages, the invention enables the production of vertically conducting gallium nitride material devices even when the device includes a non-conducting layer. In particular, it is possible to produce vertically conducting devices with silicon substrates that include such non-conducting layers. Silicon substrates are particularly desirable because they are readily available, relatively inexpensive, and may be processed using known techniques.
Furthermore, the vertical conducting devices of the invention may be formed with smaller dimensions than similar functioning horizontal devices due to the presence of fewer topside contacts on vertically conducting devices. Utilizing smaller device dimensions may enable more devices to be formed on a given wafer.
Also, the backside contact formed using the methods of the invention may have other advantageous functions. In some cases, the backside contact can function as a heat sink which removes thermal energy generated during the operation of the device. Also, the backside contact may function as a reflective layer which can enhance output efficiencies of optoelectronic devices.
It should be understood that not every embodiment of the invention has all of the advantages described herein. Other advantages, aspects, and features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.